Organic photoconductors spectrally sensitized with merocyanine dyes containing a triazolo- or tetrazolo-(1,5-a)pyrimidin-7(6h)-one nucleus

ABSTRACT

ORGANIC PHOTOCONDUCTORS ARE SPECTRALLY SENSITIZED WITH MEROCYANINE DYES WHICH FEATURE A TRIAZOLO- OR TETRAZOLO (1,5-A)PYRIMIDIN-7(6H)-ONE NUCLEUS.

United States Patent Oflice Patented Dec. 19, 1972 3,706,555 ORGANIC PHOTOCONDUCTORS SPECTRALLY SENSITIZED WITH NIEROCYANINE DYES CONTAINING A TRIAZOLO- R TETRAZOLO- [1,5-a]PYRlMIDIN-7(6H)-0NE NUCLEUS Donald W. Heseltine and Carl H. Eldredge, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Aug. 11, 1971, Ser. No. 170,972 Int. Cl. G03g 5/02, 5/06 US. Cl. 96-1.6 21 Claims ABSTRACT OF THE DISCLOSURE Organic photoconductors are spectrally sensitized with merocyanine dyes which feature a triazoloor tetrazolo [1,5-a] pyrimidin-7(6H)-one nucleus.

This invention relates to electrophotography, and more particularly to materials and elements useful in the electrophotographic process.

Elements useful in the electrophotographic process commonly comprise an electrically conductive support bearing a stratum including a photoconductive insulating layer which has a resistivity substantially greater in the dark than in light actinic thereto. Such elements can be used in electrophotographic processes, for example, by first adapting the element in the dark to obtain a uniformly high resistivity in the photoconductive insulating layer, and electrostatically charging the element in the dark to obtain a relatively high potential which may be either negative or positive in polarity. The elements can then be exposed to a light pattern which lowers the resistivity and thereby the charge density of the illuminated areas imagewise in proportion to the intensity of illumination incident upon each point of the illuminated areas. A latent electrostatic image is obtained. Visible images can be formed from the latent electrostatic image in any convenient manner, such as by dusting with a finely divided, fusible pigment the particles of which bear an electrostatic charge opposite that remaining on the surface of the photoconductive insulating layer. Thereafter, the pigment particles can be fused to the surface to provide a permanent image.

Various photoconductive substances have been employed in photographic elements and processes of the type described above. Typical inorganic photconductive materials include selenium and zinc oxide. Such inorganic photoconductive materials have inherent disadvantages, such as an inability to be readily adapted to reflex copying systems, or to produce images on transparent supports except by indirect means. Organic photoconductors avoid such disadvantages, but, generally have relatively poor sensitivity to visible radiation. It has been proposed to increase the spectral sensitivity of organic photoconductors with certain cyanine or merocyanine dyes, for example, such as listed in Table D hereinafter. The spectral sensitivity imparted by such dyes has been very weak. It therefore appears highly desirable to provide effective spectral sensitizers for organic photoconductors.

One object of this invention is to provide sensitized organic photoconductors.

Another object of this invention is to provide spectrally sensitized organic photoconductor materials.

Still another object of the invention is to provide compositions of matter comprising organic photoconductors and certain spectral sensitizers.

A further object of this invention is to provide compositions of matter comprising organic photoconductor, binder and certain spectral sensitizers for the organic photocondoctor.

Still another object of this invention is to provide an electrophotographic material including a conductive support having coated thereon an insulating layer containing spectrally sensitized organic photoconductor.

A further object of this invention is to provide methods for spectrally sensitizing organic photoconductors.

Still other objects of this invention will be apparent from the following disclosure and the appended claims.

In accordance with this invention, organic photoconductors are spectrally sensitized with merocyanine dyes comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined together by a dimethine linkage; the first of said nuclei being a triazolo (1,5-a)pyrimidin-7(6H)-one nucleus or a tetrazolo(1,5-a) pyrimidin-7(6H)-one nucleus, which first nucleus is joined at the 6-carbon atom thereof to said linkage. Preferably, the second nucleus is a desensitizing nucleus of the type used in the production of cyanine dyes joined at a carbon atom thereof to said linkage to complete said dye.

The preferred merocyanine dyes employed in this invention are represented by the following general formula:

wherein n represents a positive integer of from 1 to 2; L represents a methine linkage, e.g., CH=,

C(C H etc.; R represents an alkyl group, including substituted alkyl, (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., and substituted alkyl groups, (preferably a substituted lower alkyl containing from 1 to 4 carbon atoms), such as a hydroxyalkyl group, e.g., B-hydroxyethyl, w-hydroxybutyl, etc., an alkoxyalkyl group, e.g., fl-methoxyethyl, w-butoxybutyl, etc., a carboxyalkyl group, e.g., fi-carboxyethyl, w-carboxybutyl, etc., a sulfoalkyl group, e.g., fl-sulfoethyl, w-sulfobutyl, etc., a sulfatoalkyl group, e.g., fl-sulfatoethyl, w-sulfatobutyl, etc., an acyloxyalkyl group, e.g., fi-acetoxyethyl, 'y-acetoxypropyl, w-butyryloxybutyl, etc., an alkoxycarbonylalkyl group, e.g., fi-methoxycarbonylethyl, w-ethoxycarbonylbutyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc., and the like; an alkenyl group, e.g., allyl, l-propenyl, Z-butenyl, etc., or, an aryl group, e.g., phenyl tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; R represents an alkyl group, including substituted alkyl, (preferably a lower alkyl containing from 1 to 4 carbon atoms), e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, cyclohexyl, decyl, dodecyl, etc., or an aralkyl group, e.g., benzyl, phenethyl, etc.; or an aryl group, e.g., phenyl, tolyl, naphthyl, methoxyphenyl, chlorophenyl, etc.; D represents a nitrogen atom or a methine group such as -CH=, C(CH C(C H etc.; and Z represents the nonmetallic atoms necessary to complete a heterocyclic nucleus of the type used in cyanine dyes, preferably a desensitizing nucleus, containing from 5 to 6 atoms in the heterocyclic ring, which nucleus may contain a second hetero atom such as oxygen, sulfur, selenium or nitrogen, such as used in cyanine dyes, and including the following nuclei: a thiazole nucleus, e.g., thiazole, 4- methylthiazole, 4-phenylthiazole, S-methylthiazole, 5- phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2-thienyl)thiazole, benzothiazole, 4-chlorobenzothiazole, 4- or S-nitrobenzothiazole, S-chorobenzothiazole, 6- chlorobenzothiazole, 7-chlorobenzothiazo1e, 4-methylbenzothiazole, S-methylbenzothiazole, 6-methylbenzothiazole, S-nitrobenzothiazole, fi-nitrobenzothiazole, -bromobenzothiazole, fi-bromobenzothiazole, 5-chloro-6-nitrobenzothiazole, 4-phenylbenzothiazole, 5-phenylbenzothiazole, 4- methoxybenzothiazole, S-methoxybenZothiazole, 6-methoxybenz'othiazole, 5-iodobenzothiazole, 6-iodobenzothiazole, 4-ethoxybenzothiazole, S-ethoxybenzothiazole, tetrahydrobenzothiazole, 5,G-dimethoxybenzothiazole, 5,6-di-' oxymethylenebenzothiazole, S-hydroxybenzothiazole, 6- hydroxybenzothiazole, naphtho[2,1-d]thiazole, naphtho 1,2-d] thiazole, naphtho [2,3-d] thiazole, S-methoxynaphtho[2,3-d]thiazole, 5-ethoxynaphtho[1,2-d]thiazole, 8- methoxynaphtho [2,l-d]thiazole, 7 methoxynaphtho [2,1- d]thiazole, 4-methoxythianaphtheno-7,6',4,5-thiazole, nitro group substituted naphthothiazoles, etc.; an oxazole nucleus, e.g., 4-methyloxazole, 4-nitrooxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-dimethyloxazole, S-phenyloxazole, benzooxazole, 5-chlorobenzoxazole, S-methylbenzoxazole, 5- phenylbenzoxazole, 5- or 6-nitrobenzoxazole, 5-chloro-6- nitrobenzoxazole, 6-methylbenzoxazole, 5,6-dimethyl- 'benzoxazole, 4,6-dimethylbenzoxazole, S-methoxybenzoxazole, 5 ethoxybenzoxazole, 5 chlorobenzoxazole, 6- methoxybenzoxazole, S-hydroxybenzoxazole, 6-hydroxybenzoxazole, naphtho[2,l-d]oxazole, naphtho[1,2-d]oxazole, nitro group substituted naphthoxazoles, etc.; a selenazole nucleus, e.g., 4-methylselenazole, 4-nitroselenazole, 4-phenylselenazole, benzoselenazole, S-chlorobenzoselenazole, S-methoxybenzoselenazole, S-hydroxybenzoselenazole, 5- or 6-nitrobenzoselenazole, 5-chloro-6-nitrobenzoselenazole, tetrahydrobenzoselenazole, naphtho [2,1-d]selenazole, naphtho[1,2-d1selenazole, nitro group substituted naphthoselenazoles, etc.; a thiazoline nucleus, e.g., thiazoline, 4-methylthiazoline, 4-nitrothiazoline, etc.; a pyridine nucleus, e.g., 2-pyridine, S-methyl-Z-pyridine, 4-pyridine, 3-methyl-4-pyridine, nitro group substituted pyridines, etc.; a quinoline nucleus, e.g., 2-quinoline, 3- methyl-Z-quinoline, 5-ethy1-2-quinoline, 6-chloro-2-quinoline, 6-nitro-2-quinoline, 8-chloro-2-quinoline, 6-methoxy- 2-quinoline, S-ethoxy-Z-quinoline, 8-hydroxy-2-quinoline, 4-quinoline, 6-methoxy-4-quinoline, 6-nitro-4-quinoline, 7- methyl-4-quinoline, 8-chloro-4-quinoline, l-isoquinoline, 6 nitro 1 isoquinoline, 3,4 dihydro 1 isoquinoline, 3-isoquinoline, etc.; a 3,3-dialkylindolenine nucleus, preferably having a nitro or cyano substituent, e.g., 3,3-dimethyl-S- or G-nitroindolenine, 3,3-dimethyl-5- or 6-cyanoindolenine, etc.; and, an imidazole nucleus, e.g., imidazole, l-alkylimidazole, 1-alkyl-4-phenylimidazole, 1-alkyl-4,5- dimethylimidazole, benzimidazole, l-alkylbenzimidazole, l-aryl-5,6-dichlorobenzimidazole, l-alkyl-1H-naph[1,2+d] imidazole, 1-aryl-3H-naphth[l,2-d]imidazole, l-alkyl- 5-methoxy-1H-naphth[2,l-d]imidazole, etc., an imidazo [4,5-b]quinoxaline nucleus, e.g., a 1,3-dialkylimidazo [4,5-b]quinoxaline such as l,3-diethylimidazo[4,5-b] quinoxaline, 6-chloro-1,3-diethylimidazo[4,5-b]quinoxaline, etc., a 1,3-dialkenylimidazo[4,5-b]quinoxaline such as 1,3-diallylimidazo[4,5-b]quinoxaline, 6-chloro-l,3-diallylimidazo[4,5-b]quinoxaline, etc., a 1,3-diarylimidazo [4,5-b]quinoxaline such as l,3-diphenylimidazo[4,5-b] quinoxaline, 6-chloro-1,3-diphenylimidazo [4, 5-b] quinoxaline, etc.; a 3,3-dialkyl-3H-pyrrolo[2,3-b]pyridine nucleus, e.g., 3,3-dimethyl-3H-pyrrolo[2,3-b]pyridine, 3,3- diethyl-BH-pyrrolo[2,3-b]pyridine, etc.; a thiazole[4,5-b] quinoline nucleus; and the like. The nuclei wherein Z in above Formula I represents the atoms necessary to complete a desensitizing nucleus such as a nitro group substituted thiazole, oxazole, selenazole, thiazoline, pyridine, quinoline, 3,3-dialkylindolenine or imidazole nucleus; or a 3,3-dialkyl-3H-pyrrolo[2,3-b]pyridine nucleus and the like; provide particularly efficaciousspectral sensi tizers for organic photoconductors in accordance with this invention. Dyes containing such desensitizing nuclei, and more particularly those wherein the said first nucleus is a triazolo [1,5-a1pyrimidin-7(6H)-one nucleus, are the prelisted below:'

ferred dye species herein. Representative useful dyes are As used herein and in the appended claims, desensitizing nucleusF-refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from-0.0110 0.2 grams dye per mole of silver, cause by electron trapping at least about an 80 percent loss in the blue speed of the emulsion when sensitometrically exposed and developed three minutes in Kodak developer D-l9 at 20 C., the composition of which is well known. Preferably, the electron-accepting nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described above, essentially completely desenitize the test emulsion to blue radiation. Substantially complete desensitization as used herein, results in at least a v9 0 percent, and preferably a 95 percent loss of speed to blue radiation.

The merocyanine dyes of Formula I are prepared conveniently by heating a mixture of (1) a heterocyclic compound of the formula:

R I I(CH=CH)n-1b=L-L=0 and (2) a pyrimidinone of the formula:

(III) 0 N t-A l'q H20 0 W Formula III can be readily prepared by the methods described in N. Heimbach, et al., U.S. Pat. No. 2,444,605, issued July 6, 1948;N. Heimbach, U.S. Pat. No. 2,450,397, issued Sept. 28, 1948; or as described by C. F. H. Allen, et al., J. Org. Chem. 24, 779-796 (1959).

Photographic silver halide emulsions containing the subject dyes are described in pp ants LLS-- et. 3, 8 8

issued June 1, 1971. Further details for preparing the subject dyes appear in that patent.

Dyes such as illustrated above can be used alone, or a combination of several of the above described dyes can be used to impart the desired spectral sensitivity. All of them are spectral sensitizers for organic photoconductors. Suitable organic photoconductors which are effectively spectrally sensitized by such dyes include both monomeric and polymeric organic photoconductors. The invention is particularly useful in increasing the speed of organic photoconductors which are substantially insensitive, or which have low sensitivity (e.g., a speed less than 35 when tested as described in the examples below) to radiation of 400 to 700 nm.

An especially useful class of organic photoconductors is referred to herein as organic amine photoconductors. Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (1) diarylamines such as diphenylamine, dinaphthylamine, N,N-diphenylbenzidine, N-phenyl-l-naphthylamine; N phenyl-2-naphthylamine; N,N'-diphenyl-p-phenylenediamine; 2-carboxy-5-chloro-4'- methoxydiphenylamine; p-anilinophenol; N,N'-di-2-naphthyl-p-phenylene diamine; 4,4'-benzylidene-bis(N,N-diethyl-m-toluidine), those described in Fox U.S. Pat. 3,240,- 597 issued Mar. 15, 1966, and the like, and (2) triarylamines including (a) nonpolymeric triarylamines, such as triphenylamine, N,N,N,N'-tetraphenyl-m-phenylenediamine; 4-acetyltriphenylamine, 4-hexanoyltriphenylamine; 4-lauroyltriphenylamine; 4-hexyltriphenylamine, 4- dodecyltriphenylamine, 4,4'-bis(diphenylamino)-benzil, 4,4- bis(diphenylamino)benzophenone, and the like, and (b) polymeric triarylamines such as poly[N,4"-(N,N,N"triphenylbenzidine)]; polyadipyltriphenylamine, polysebacyltriphenylamine; polydecamethylenetriphenylamine; poly-N-(4 vinylphenyl)-diphenylamine, poly-N-(vinylphenyl)-a,a'-dinaphthylamine and the like. Other useful amine-type photoconductors are disclosed in US. Pat. 3,180,730, issued Apr. 27, 1965.

Other very useful photoconductive substances capable of being spectrally sensitized in accordance with this invention are disclosed in Fox US. Pat. 3,265,496 issued Aug. 9, 1966, and include those represented by the following general formula:

G- N-A- Q wherein A represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear, (e.g., phenylene, naphthylene, biphenylene, binaphthylene, etc.), or a substituted divalent aromatic radical of these types wherein said substitutent can comprise a member such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.) an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; A represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.); or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from 1 to about 6 carbon atoms (e.g., acetyl, propionyl, butyryl, etc), an alkyl group having from 1 to about 6 carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from 1 to about 6 carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro group; Q can represent a hydrogen atom, a halogen atom or an aromatic amino group, such as A'NH-; b represents an integer from 1 to about 12, and G represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, or a nitro group, or a poly(4'-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group. Certain nitrogen heterocyclic compounds are also useful photoconductors in the invention such as, for example, 1,3,5-triphenyl-Z-pyrazoline, 2,3,4,5-tetraphenylpyrrole, etc.

Polyarylalkane photoconductors are particularly useful in producing the present invention. Such photoconductors are described in US. Pat. 3,274,000; French Pat. 1,383,- 461 and in a copending application of Sens et al. Ser. No. 624,233, Photoconducti-ve Elements Containing Organic Photoconductors, filed Mar. 20, 1967, now US. Pat. 3,542,544. These photoconductors include leuco bases of diaryl or triaryl methane dye salts, 1,1,1-triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetraarylmethanes, there being substituted an amine group on at least one of the aryl groups attached to the alkane and methane moieties of the latter two classes of photoconductors which are non-leuco base materials.

Preferred polyaryl alkane photoconductors can be represented by the formula:

wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having 1 to 8 carbon atoms, hydroxy, halogen, etc. in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fiuorene moiety, for example. The amino substituent can be represented by the formula wherein each R, can be an alkyl group typically having 1 to 8 carbon atoms, a hydrogen atom, an aryl group, or together the necessary atoms to form a heterocyclic amino group typically having 5 to 6 atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E and G is preferably p-dialkylaminophenyl group. When I is an alkyl group, such an alkyl group more generally has 1 to 7 carbon atoms.

Representative useful polyarylalkane photoconductors include the compounds listed below:

methane. 11 4,4-bis(benzylethylamino)-2,2'-dimethyltriphenylmethane. 12. 4,4'-bis(diethylamino)-2,2-diethoxytriphenylmethane. 4,4-bis dimethylamino)-1,1,1-triphenylethane.

1-(4-N,N-dimethylaminophenyl)-1,1-diphenylethane.

15: 4-dirnethylaminotetraphenylmethane. 16 4-diethylaminotetraphenylmethane.

As described herein a wide variety of photoconductor compounds can be spectrally sensitized with the dyes referred to above. Some organic photoconductors will, of course, be preferred to others; but in general useful results may be obtained from substantially all of the presently known organic photoconductors.

The following Table C comprises a partial listing of US. patents describing such organic photoconductors and compositions which can be used in place of those more particularly described herein.

TABLE Inventor Issued Noe et al February 25, 1964.

Sus et al March 31, 1964.

Schlesinger... April 21, 1964. Cassiers- April 28 1964. Schlesinger June 30, 1964. -do Do.

assiers.. July 14, 1964.

Davis et a1 July 21,1964.

Ghys September 15, 1964. Cassiers. November 3, 1964. 3, 8 d0 November 24, 1964. 3, Tomanek December 1964. 3, Schlesinger. December 29, 1964. 3, 0... Do. 3, --do... Do. 3,169,060 Hoegl February 9, 1965. 3, 174, 854-.- Stumpf March 23, 1965. 3, 180, 729- Klupfel et a1 April 27, 1965. 3, 180, 730 do Do. 3, 189,447 Neugebauer June 15, 1965. 3,206,306-.- .do Se tember 14, 1965. 3,141,7 Davis et al Ju y 21, 1964. 3. 037, 861... Hoegl et al June 5, 1962. 3, 041, 165 Sus et a]--. June 26 1962. 3,066,023 Schlesinger. November 27,1962. 3,072,479 Bethe January 8, 1963. 3,047,095 Klupiel et al July 9, 1963. 3, 112, 197 Neugebauer et al November 26, 1972. 3, 113, 022 Cassiers at al December 3, 1963. 3,114,633 Schlesinger..- December 17, 1963. 3,265,497-- Kosehe et a1 August 9, 1966. 3, 274,000 Noe et al-- September 20, 1966.

The spectrally sensitized organic photoconductor compositions of this invention can, in certain arrangements, be employed in electrophotographic elements in the absence of binder. For example, the photoconductor itself is sometimes capable of film formation, and therefore requires no separate binder. An example of such film-forming photoconductor is poly(vinylcarbazole). However, the more common arrangement is to provide a binder for the spectrally sensitized organic photoconductive materials. Any suitable binder material can be utilized for the spectrally sensitized organic photoconductors of the invention. Such binders should possess high dielectric strength, and have good insulating properties (at least in the absence of actinic radiation) as well as good film forming properties. Preferred binder materials are polymers such as polystyrene, poly(methylstyrene), styrenebutadiene polymers, poly (vinyl chloride), poly(vinylidene chloride), poly(vinyl acetate), vinyl acetate-vinyl chloride polymers, poly(vinyl acetals), polyacrylic and methacrylic acid esters, polyesters such as poly(ethylene alkaryloxyalkylene terephthalates), phenol-formaldehyde resins, polyamides, polycarbonates and the like.

The photoconductive compositions of the invention can be coated on any of the electrically conductive supports conventionally used in electrophotographic processes, such as metal plates or foils, metal foils laminated to paper or plastic films, electrically conductive papers and films, papers and films coated with transparent electrically conductive resins and the like. Other useful conducting layers include thin layers of nickel coated by high vacuum deposition and cuprous iodide layers as described in US. Pat. 3,245,833. Transparent, translucent or opaque support material can be used. Exposure by reflex requires that the support transmit light while no such requirement is necessary for exposure by projection. Similarly transparent supports are desired if the reproduction is to be used for projection purposes; translucent supports are preferred for reflux prints; and opaque supports are adequate if the image is subsequently transferred by any means to another support, or the reproduction is to be used as a printing plate for preparing multiple copies of the original.

The quantity of the above-described dye required to spectrally sensitize an organic photoconductor varies with the results desired, the particular dye used, and the particular organic photoconductor used. Best results are obtained with about .01 to 10 parts by weight dye and about 1 to 75 parts by weight of the organic photoconductor based on the photoconductive composition. Binder can be employed in such compositions, when desired, at preferred ranges of 25 to 99 parts by weight. In addition, the composition can contain other sensitizers, either spectral sensitizers or speed increasing compounds, or both.

As used herein and in the appended claims, the terms insulating and electrically conductive have reference to materials the surface resistivities of which are greater than 10 ohms per square unit (e.g., per square foot) and less than 10 ohms per square unit (e.g., per square foot) respectively.

Coating thicknesses of the photoconductive compositions of the invention on a support can vary widely. As a general guide, a dry coating in the range from about 1 to 200 microns is useful for the invention. The preferred range of dry coating thickness is in the range from about 3 to 50 microns.

To produce a reproduction of an image utilizing the electrophotographic elements of our invention, the photoconductive layer is preferably dark adapted, and then is charged either negatively or positively by means of, for example, a corona discharge device maintained at a potential of from 6000-7000 volts. The charged element is then exposed to light through a master, or by reflex in contact with a master, to obtain an electrostatic image corresponding to the master. This invisible image may then be rendered visible by being developed by contact with a developer including a carrier and toner. The carrier can be, for example, small glass or plastic balls, or iron powder. The toner can be, for example, a pigmented thermoplastic resin having a grain size of from about 1-100 which may be fused to render the image permanent. Alternatively, the developer may contain a pigment or pigmented resin suspended in an insulating liquid which optionally may contain a resin in solution. If the polarity of the charge on the toner particles is opposite to that of the electrostatic latent image on the photoconductive element, a reproduction corresponding to the original is obtained. If, however, the polarity of the toner charge is the same as that of the electrostatic latent image, a reversal or negative of the original is obtained.

Although the development techniques described hereinabove produce a visible image directly on the electrophotographic element, it is also possible to transfer either the electrostatic latent image, or the developed image to a second support which may then be processed to obtain the final print. All of these development techniques are well known in the art and have been described in a number of US. and foreign patents.

This invention is further illustrated by the following representative examples.

EXAMPLES These examples illustrate the great increase in speed of organic photoconductors when the dyes employed in this invention are added thereto. This increase in speed is due to the spectral sensitivity imparted to the photoconductor by the dyes described herein. The examples show that the maximum sensitivity (abs max.) occurs in most cases at wavelengths ranging from about 530 to 540 mm.

A series of solutions are prepared consisting of 5.0 ml. methylene chloride (solvent); 0.15 g. 4,4'-bis(diethylamino)-2,2'-dimethyltriphenylmethane (organic photoconduc- -50 gp lyester composed of terephthalic acid and a glycol mixture comprising a 9:1 weight ratio of 2,2- bis[4-(2-hydroxyethoxy) phenyl] propane and ethylene glycol (binder) and 0.0065 g. of the spectral sensitizing dye indicated by identifying number which is given above. Each solution is coated on an aluminum surface maintained at 25 C. and dried. All operations are carried out in a darkened room. A sample of each coating is uniformly charged by means of a corona to a potential of about 600 volts and exposed through a transparent member bearing a pattern of varying optical density to a 3000 K. tungsten source. The resultant electrostatic image pattern is then rendered visible by cascading a developer composition comprising finely divided colored thermoplastic electrostatically responsive toner particles carried on glass beads over the surface of the element. The image is then developed by deposition of the toner in an imagewise manner on the element. (Other development techniques such as those described in US. 2,786,439; 2,786,- 440; 2,786,441; 2,811,465; 2,874,063; 2,984,163; 3,040,- 704; 3,117,884; Re. 25,779; 2,297,691; 2,551,582; and in RCA Review, vol. (1954) pages 469-484, can be used with similar results.) An image is formed on each sample as indicated in Table I. Another sample of each coating is tested to determine its electrical speed and maximum sensitivity peak. This is accomplished by giving each element a positive or negative charge (as indicated in Table I) with a corona source until the surface potential, as measured by an electrometer probe, reaches 600 volts. It is then exposed to light from a 3000 K. tungsten source of -foot candle illuminance at the exposure surface. The exposure is made through a stepped density gray scale. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial potential, V to some lower potential, V, whose exact value depends on the actual amount of exposure in meter'caudle-seconds received by the area. The results of these measurements are plotted on a graph of surface potential V vs. log exposure for each step. The actual speed of each element is expressed in terms of the reciprocal of the exposure required to reduce the surface potential by 100 volts. Hence, the speeds given in Table I are the numerical expression of 10 divided by the exposure in meter-candle-seconds required to reduce the 600 volts charged surface potential by 100 volts. The results are shown in Table I below.

Referring to the above Table I, it will be seen that the control example containing the same photoconductor but no dye shows speeds of only 32 and 23 for the positively and negatively charged surfaces, respectively, whereas the corresponding values for those of the invention represented by Examples 1-7 are clearly of a different order of magnitude. For example, the speed shown by Example 1 (Dye No. 1) is 1200 and 320 for the positively and negatively charged surfaces, respectively, with maximum sensitivity peak at 530 nm., thus indicating a great speed increase over that of the control. Also of great significance is the extension of the absolute sensitivity to the region of about 530 nm. or more.

Similar results to those shown in above Table I are obtained, when, for example, the organic photoconductor 4,4 bis(diethylamino) 2,2 dimethyltriphenylmethane is replaced with 0.15 g. of triphenylamine (using the p-toluene-sulfonate salt of each dye), or 1,3,5-triphenyl- 2-pyrazoline, or 2,3,4,5-tetraphenylpyrrole, or 4,4-bis-diethylaminobenzophenone or when other dyes of the invention embraced by Formula I above are used. These results show that the dyes of this invention effectively spectrally sensitize a wide variety of organic photoconductors. The above mentioned photoconductors when used alone have very low photoconductive speed to visible light. However, as shown by the tests, the combination of the dyes of the invention with the photoconductors of the invention provide compositions and elements of outstanding speed and excellent quality of image.

This invention is highly unexpected because dyes previously suggested for spectral sensitizers impart weak spectral sensitization to organic photoconductors. Typical dyes proposed by the prior art as spectral sensitizers, which produce weak spectral sensitization in these systems, are shown in Table D following:

In contrast, as indicated previously, the dyes of this invention are inoperable as spectral sensitizers for conventional negative type photographic silver halide emulsions because they strongly desensitize such emulsions.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. A composition of matter comprising an organic photoconductor sensitized with a merocyanine dye comprising first and second 5- to 6-membered nitrogen containing heterocyclic nuclei joined by a dimethine linkage; the first of said nuclei being selected from the group consisting of a triazolo[1,5-a]pyrimidin-7(6H) one nucleus and a tetrazolo[l,5-a]pyrimidin-7(6H)-one nucleus, said first nucleus being joined at the 6-carbon atom thereof to said linkage, said second nucleus being of the type used in cyanine dyes.

2. A composition of matter as defined by claim 1 wherein said second nucleus of said dye is a desensitizing nucleus.

3. A composition of matter as defined in claim 2 wherein said desensitizing nucleus of said dye is substituted by a nitro group on a carbon atom thereof.

4. A composition of matter as defined in claim 2 wherein said desensitizing nucleus of said dye is an irnidazo [4,5-b] -quinoxaline nucleus.

5. A composition of matter as defined in claim 2 wherein said desensitizing nucleus of said dye is a 3,3-dialkyl- 3H-pyrrolo[2,3-b1pyridine nucleus.

6. A composition of matter comprising an organic photoconductor sensitized with a merocyanine dye selected from those represented by the following general formula:

wherein n represents a positive integer of from 1 to 2; L

represents a methine linkage, R represents a member selected from the group consisting of an alkyl group, an alkenyl group and an aryl group; R represents a member selected from the group consisting of an alkyl group and an aryl group; D represents a member selected from the group consisting of a nitrogen atom and a methine group; and Z represents the non-metallic atoms necessary to complete a nucleus containing to 6 atoms in the heterocyclic ring and of the type used in cyanine dyes.

7. A composition of matter as defined by claim 6 wherein said Z represents the non-metallic atoms required to complete a desensitizing nucleus.

8. A composition of matter as defined by claim 6 wherein said Z represents the non-metallic atoms required to complete a nucleus selected from the group consisting of a nitrobenzothiazole nucleus; a nitrobenzoxazole nucleus; 21 nitrobenzoselenazole nucleus; an imidazo[4,5 -b]quinoxaline nucleus; and a 3,3 dialkyl-3(H)-pyrrolo[2,3-b] pyridine nucleus.

9. A composition of matter as defined in claim 6 wherein said D represents a nitrogen atom.

10. A composition of matter as defined in claim 6 wherein said D represents a methine group.

11. A composition of matter comprising an organic photoconductor sensitized with a merocyanine dye selected from the group consisting of 6- 1,3-diallylimidazo [4,5-b] -quinoxalin-2( 3H ylidene ethylidene] -5-methyl-s-triazolo 1,5-a] pyrimidin-7 (6H)-one,

5-methyl-6-[ 1,3,3-trimethyl-5-nitro-2 3H) -indolinylidene)ethylidene] -s-triazolo[ 1,5-a] -pyrimidin-7 6H)- one,

6-[ 3-ethyl-6-nitro-2-benzothiazolinylidene) -ethylidene] S-methyl-s-triazolo 1,5-a] pyrimidin-7 (6H )-one,

5-methyl-6- 1,3,3-trimethyl-1 (H) -pyrrolo [2,3-b]

pyridin-2- (3H) -ylidene) ethylidene] -s-triazolo[ 1,5-a] pyrimidin-7(6H)-one,

6- 3-ethyl-6-nitro-2-benzothiazolinylidene ethylidene]- 5-methyltetrazolo[ 1,5-a] pyrimidin-7 6H -one,

6-[ (6-chloro-1 ,3-diphenylimidazo [4,5 -b quinoxolin- 2(3H)ylidene)ethylidene]-5-methyltetrazolo[1,5-a]

. pyrimidin-7(6H)-one,

6-[ (6-chloro-1,3-diphenylimidazo [4,5-b] quinoxolin-2- -(3H)ylidene ethylidene] -5-methyl-s-triazolo 1,5-a] pyrimidin-7(6H)-one,

6- 1-ethylnaphtho[ 1,2-d] thiazolin-Z-ylidene )ethylidene)ethylidene] -5-methyl-s-triazolo 1,5-a1pyrimidin- 7(6H)-one,

6-[ 1,3-diethylimidazo [4,5-b] quinoxolin-2(3H)ylidene) ethylidene] -5-methyltetrazolo[ 1,5-a] pyrimidin-7 (6H)- one,

5-methyl-6-[ 1 ,3,3-trimethyl-5-nitro-2( 3H) -indolinylidene)ethylene]tetrazolo[ 1,5-a] pyrimidin-7(6H)-one,

5-methy1-6- 1,3,3-trimethy1- lH-pyrrolo[2,3,b] pyridin- 2( 3H)-ylidene )ethylidene] tetrazolo 1,5-a] pyrimidin- 7-(6H)-one; and,

said organic photoconductor is 4,4-bis(diethylamino)-2,

2'-dimethyltriphenylmethane.

12. A composition as defined by claim 6 wherein said organic photoconductor has the following formula:

wherein each of D, E and G is an aryl group and J is selected from the group consisting of a hydrogen atom,

an alkyl group and an aryl group, at least one of D, E and G containing an amino substituent selected from the group consisting of a secondary amino group and a tertiary amino group.

'13. A composition as defined by claim 6 wherein said 12 organic photoconductor is selected from the group consisting of: triphenylamine; 1,3,5-triphenyl-2-pyrazoline; 4, ,4'-ibits(diethylam-ino)-2;2'-dimethyltriphenylaminei 2,3, S-tetraphenylpyrrole; and 4,4-bis-diethylaminobenzophenone.

14. A composition as defined by claim 6 wherein said photoconductor comprises from 1 to parts by weight of said composition, said photoconductor being spectrally sensitized with from .01 to 10 parts by weight of said composition of said merocyanine dye.

15. A composition of matter comprising from 1 to 75 parts by weight of an organic photoconductor selected from the group consisting of: triphenylamine; 1,3,5-triphenyl-2-pyrazoline; 4,4'-bis-di.ethylamino-2,2'-dimethyltriphenylmethane; 2,3,4,5-tetraphenylpyrrole; 4,4'-bis-diethylaminobenzophenone; said organic photoconductor being spectrally sensitized with from .01 to 10 parts by weight of 6- 1,3-diallylimidazo[4,5-b] quinoxalin-2(3H)- ylidene)ethy1idene]-5-methyl-s-triazolo[1,5 a] pyrimidin- 7(6H)-one.

16. A composition of matter as defined in claim 15 wherein said organic photoconductor and said dye are dispersed in from 25 to 99 parts by weight of a polyester of terephthalic acid and a glycol mixture consisting of a 9:1 weight ratio of 2,2-bis-[4-(2-hydroxyethoxy)-phenyl]- propane and ethylene glycol as insulating binder.

17. An electrophotographic element comprising a conductive support having thereon a layer comprising an organic photoconductor in an insulating binder, said organic photoconductor being spectrally sensitized with a merocyanine dye comprising first and second 5- to 6- membered nitrogen containing heterocyclic nuclei joined by a dimethine linkage; the first of said nuclei being selected from the group consisting of a triazolo[1,5-a] pyrimidin-7(6H)-one nucleus and a tetrazolo[1,5-a] pyrimidin-7(6H)-one nucleus, said first nucleus being joined at the '6-carbon atom thereof to said linkage, said second nucleus being of the type used in cyanine dyes.

18. An electrophotographic element as defined in claim 17 wherein said second nucleus of said dye is an electronaccepting nucleus.

19. An electrophotographic element as defined in claim 17 wherein said second nucleus of said dye is selected from the group consisting of: a nitro group substituted nucleus and an imidazo[4,5-b] quinoxaline nucleus.

20. An electrophotographic element as defined inclaim 17 wherein said organic photoconductor is selected from the group consisting of: a triphenylamine; a 1,3,5-triaryl- Z-pyrazoline; a 4,4'-bis(dialkylamino)-2,2'-dialky1triarylamine; a 2,3,4,5-tetraarylpyrrole; and a 4,4'-bis-dialky1- aminobenzophenone,

21. An electrophotographic element as defined in claim 20 wherein said organic photoconductor comprises from 1 to 75 parts by weight of said composition, said photoconductor being spectrally sensitized with from .01 to 10 parts by weight of said composition of said merocyanine dye.

References Cited UNITED STATES PATENTS 3,565,615 2/1971 Brooker et a1. 96-1.6

3,565,616 2/ 1971 {Webster et al. 96-1.6

3,582,348 6/1971 Heseltine et a1. 96-141 3,528,811 9/1970 Webster et a1. 9'6141 FOREIGN PATENTS 1,194,255 7/1960 Germany 961.6

GEORGE F. LESMES, Primary Examiner R. E. MARTIN, Jr., Assistant Examiner 

